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    SubjectRe: [PATCH] tracing/events: Add module tracepoints
    Frederic Weisbecker wrote:
    > On Tue, Jul 21, 2009 at 04:56:33PM +0800, Li Zefan wrote:
    >> Add trace points to trace module_load, module_free, module_get,
    >> module_put and module_request, and use trace_event facility
    >> to get the trace output.
    >>
    >> Here's the sample output:
    >>
    >> TASK-PID CPU# TIMESTAMP FUNCTION
    >> | | | | |
    >> <...>-42 [000] 1.758380: module_request: fb0 wait=1 call_site=fb_open
    >> ...
    >> <...>-60 [000] 3.269403: module_load: scsi_wait_scan
    >> <...>-60 [000] 3.269432: module_put: scsi_wait_scan call_site=sys_init_module refcnt=0
    >> <...>-61 [001] 3.273168: module_free: scsi_wait_scan
    >> ...
    >> <...>-1021 [000] 13.836081: module_load: sunrpc
    >> <...>-1021 [000] 13.840589: module_put: sunrpc call_site=sys_init_module refcnt=-1
    >> <...>-1027 [000] 13.848098: module_get: sunrpc call_site=try_module_get refcnt=0
    >> <...>-1027 [000] 13.848308: module_get: sunrpc call_site=get_filesystem refcnt=1
    >> <...>-1027 [000] 13.848692: module_put: sunrpc call_site=put_filesystem refcnt=0
    >> ...
    >> modprobe-2587 [001] 1088.437213: module_load: trace_events_sample F
    >> modprobe-2587 [001] 1088.437786: module_put: trace_events_sample call_site=sys_init_module refcnt=0
    >>
    >>
    >> Note:
    >>
    >> - the taints flag can be 'F', 'C' and/or 'P' if mod->taints != 0
    >>
    >> - the module refcnt is percpu, so it can be negative in a specific cpu
    >>
    >> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
    >
    >
    > Nice.
    >
    > Just two worries about it.
    >
    > The ring buffer are flushed on module unloading right?
    > That won't make it easy to perform module event tracing.
    >

    Yes, but only when the module has "_ftrace_events" section.
    They are ext4 and gfs2 for the current kernel.

    > Also the events selftests do a lot of random things to trigger
    > each kind of events, I guess some new others will be needed to
    > tests these, unless they will seem to fail on every selftests.
    > Although I can't imagine a module loading/unloading for
    > every ftrace event selftest... I guess these will require
    > a specific treatement and also will need to be selftested once
    > the filesystem is set to be able to load modules.
    >

    It's nice to have more selftests but I don't think it is a
    necessity.

    Actually the events selftests just confirm the events won't
    crash the system, and no trace entries are generated by them
    in the selftests.



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